UNIVERSITY  OF  CALIFORNIA  Agricultural  Experiment  Station 

College  of  agriculture  e.  j.  wickson,  acting  director 

BERKELEY,   CALIFORNIA 


CIRCULAR  No.  32 

(July,  1907.) 


WHITE    FLY    ERADICATION 


BY 

C.  W.  WOODWORTH. 


Since  the  publication  of  Circular  30,  "White  Fly  in  California," 
by  this  Experiment  Station,  the  insect  has  gone  through  another  full 
generation.  Very  strenuous  though  misdirected  efforts  have  been 
made  towards  its  eradication,  but  the  problem  to-day  is  many  fold 
more  difficult,  and  the  possibility  of  its  suppression  much  more  doubt- 
ful than  a  month  ago. 

A  very  large  proportion  of  the  insects  have  been  destroyed  through 
these  efforts,  but  not  one  acre  of  infested  territory  has  been  cleared, 
and  it  requires  just  as  thorough  defoliation  where  there  are  but  five 
white  flies  as  though  there  were  five  thousand.  Moreover,  for  the 
remainder  of  the  summer,  winged  individuals  will  be  continually 
coming  forth,  making  the  chances  of  its  spreading  to  other  localities 
a  very  serious  matter. 

We  are  now,  therefore,  confronted  with  a  new  set  of  conditions  and 
should  take  a  new  view  of  the  problem  and  prepare  to  meet  the  new 
conditions  wisely,  avoiding  the  mistakes  of  the  past  campaign. 

What  Has  Been  Done. 

The  white  fly  was  discovered  early  in  May,  and  the  first  work  to- 
wards its  eradication  was  done  on  the  22nd  of  June.  The  greater  part 
of  the  defoliation,  however,  was  done  during  the  present  month.  How 
large  the  task  was,  one  can  have  little  conception  from  a  cursory  ex- 
amination of  the  town.  An  examination  of  the  map  presented  in  this 
circular  will  enable  one  to  get  a  comprehensive,  though  still  inade- 
quate, idea  of  its  magnitude. 


"We  have  attempted  in  this  map  to  show  the  location  and  present 
condition  of  every  citrus  tree  in  Marysville.  The  map  is  probably 
not  absolutely  accurate,  since  it  was  drawn  from  what  could  be  made 
out  without  entering  the  lots,  and  very'  likely  a  few  trees  have  been 
overlooked,  but  it  will  give  a  fair  idea  of  the  present  situation. 


Fig.  1.     The  method  of  defoliation  most  commonly  adopted. 

Besides  the  citrus  trees,  we  have  indicated  in  this  map  the  position 
of  the  electric  and  steam  railways,  because  they  may  be  supposed  to 
afford  the  most  ready  means  of  transporting  the  insect  to  other  parts 
of  the  State.  The  territory  that  was  found  badly  infested  this  spring, 
all  lay  in  a  strip  along  the  street-car  tracks  between  B  and  I  streets; 
in  no  case  as  far  as  our  observations  went  were  the  over-wintering 
individuals  found  farther  than  two  blocks  from  the  street-car  tracks. 
The  flies  of  the  spring  generation,  however,  spread  the  infestation  two 
or  three  blocks,  extending  their  range  at  certain  points  to  the  Southern 


Pacific  tracks.  We  did  not  discover  any  evidence  of  the  insect  on  the 
other  side  of  these  railroad  tracks.  It  would,  however,  be  impossible 
to  say  that  they  had  not  passed  beyond.  We  have  but  little  doubt  that 
the  more  outlying  districts  have  always  been  free  from  the  pest. 
A  study  of  the  map  will  show  that  these  trees  were  defoliated  as 
promptly,  and  nearly  as  completely,  as  the  center  of  the  town.  The 
method  of  defoliation  ordered  by  the  State  Commissioner  of  Horti- 
culture was  that  illustrated  in  fig.  11.  The  majority  of  the  citrus 
trees  in  town  are  high  pruned,  so  that  the  work  must  be  done  from  a 
step-ladder.     Fig.  1,  from  a  photograph  taken  by  Professor  Clarke 


Fig.  2.     The  top  of  a  defoliated  tree,  showing  careless  work. 


on  July  12,  is  a  very  good  illustration  of  the  method  of  handling  the 
trees.* 

Some  of  the  work  was  well  and  carefully  done,  but  there  are  many 
examples  of  very  bad  practice.  A  typical  case  of  bad  work  is  shown 
in  fig.  2.  There  was  very  little  skilled  labor  to  be  had,  and  the  owners 
themselves,  in  most  cases,  knew  but  little  about  the  handling  of  trees. 
A  man  with  a  saw  and  a  white-wash  brush,  if  he  made  a  pretense  of 
knowing  about  trees,  could  command  from  seven  to  ten  dollars  a  day. 

After  cutting  the  trees,  the  brush  was  usually  thrown  into  the 

street,  and  the  city  undertook  to  have  the  rubbish  removed.     This 

removal  of  the  brush  is  the  only  assistance  the  citizens  have  received 

in  the  work,  and  no  attempt  has  been  made  to  secure  uniformity,  either 

*  I  am  indebted  to  Professor  Clarke  for  most  of  the  photographs  in  this  circular. 


Fig.  3.     A  brush  pile  in  the  street. 


Fig.  4.     Another  larger  brush  pile. 


in  the  time  of  cutting  or  in  the  disposal  of  the  infested  leaves.  In 
some  cases  they  were  left  on  the  ground  beneath  the  trees,  and  in  other 
cases  the  city  allowed  the  brush  heaps  to  remain  in  the  streets  or  alleys 
till  the  flies  emerged  and  until  the  adjacent  trees  were  out  in  foliage 
again. 

Fig.  3  is  a  fair  example  of  this  practice.  On  the  left,  the  trees 
belonging  to  one  lot  have  been  cut  for  some  time,  the  trunks  white- 
washed and  the  brush  which  was  thrown  into  the  street  removed.  On 
the  right,  the  trees  were  just  being  defoliated  on  July  20,  the  date  the 
photograph  was  taken. 


Fig.  5.     Loading  brush  for  removal  to  the  dumps. 

The  quantity  of  the  brush  that  had  to  be  disposed  of  was  very  large, 
for  most  of  the  trees  were  quite  old,  some  upward  of  thirty  years,  and 
they  had  been  allowed  to  grow  as  large  as  they  would.  The  brush 
piles,  therefore,  on  the  sides  of  the  streets  were  often  very  large.  One 
of  the  larger  piles  is  illustrated  in  fig.  4.  In  this  case,  however,  the 
pile  is  composed  in  part  of  osage  orange,  which  also  was  cut  in  some 
cases,  though  most  of  the  osage  orange  in  town  is  still  standing. 

The  brush  was  gathered  on  wagons,  as  shown  in  fig.  5,  and  taken 
to  a  dumping  ground,  there  unloaded,  and  allowed  to  dry  ready  for 
burning.  No  precaution  was  taken  to  prevent  the  scattering  of  in- 
fested leaves  along  the  streets,  and  indeed  dried  orange  leaves  may  be 


found  almost  anywhere,  though  not  numerously  enough  to  be  very 
conspicuous. 

There  were  three  dumping  places'  used  for  the  disposal  of  the 
brush.  One  of  these  was  on  the  swampy  land  near  the  Southern 
Pacific  tracks,  within  a  hundred  yards  of  orange  trees.  This  dump- 
ing ground  was  only  used  a  short  time,  however,  though  the  brush  is 
not  yet  burned.  The  greater  part  of  this  material  was  taken  over  the 
dyke  and  unloaded  at  G  and  Second  streets.  We  show,  at  fig.  6,  a 
bird's-eye-view  of  this  dumping  ground,  taken  from  the  top  of  a  willow 
tree  along  the  dyke  near  G  street,  looking  across  the  sand-flats  where 


Fig.  6.     A  dump  heap  on  the  river. 

the  dumps  are  and  the  river  toward  the  Yuba  City  side.  To  the  left 
will  be  seen  the  ashes  of  the  trees  brought  to  the  dumps  up  to  about 
July  12,  the  rest  of  the  brush  has  accumulated  since  that  date.  The 
brush  heaps  occupy  perhaps  four  or  five  acres. 

A  rough  estimate  made  by  Professor  Clarke  and  myself  of  the 
contents  of  this  dump  pile  is  as  follows :  Brush  from  citrus  trees,  85 
per  cent. ;  osage  orange,  10  per  cent. ;  persimmon,  3  per  cent ;  privet, 
2  per  cent. ;  with  very  small  amounts  of  jasmine,  honeysuckle,  bridal- 
wreath,  rose,  fig,  and  palm. 

The  fact  that  the  white  fly  was  already  on  the  wing  in  great  num- 
bers as  early  as  the  12th  of  July,  and  that  practically  all  of  the  brush 
shown  in  fig.  6  was  taken  there  after  that  date,  shows  that  the  insect 
was  given  ample  time  to  develop  before  defoliation.  The  presence  of 
new  foliage  on  trees  all  over  town  shows  further  that  the  insects  had 


Fig.  7.     Orange  trees  in  foliage  and  defoliated. 


Fig.  8.     Small  potted  orange  trees  that  escaped  the  inspector. 


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no  lack  of  young  foliage  on  which  to  deposit  their  eggs.  Fig.  7,  from 
a  photograph  taken  as  late  as  July  20,  illustrates  how  trees  were 
allowed  to  remain  in  foliage  long  after  the  neighboring  trees  were 
defoliated,  so  that,  as  the  new  leaves  came  out,  the  white  flies  were 
right  at  hand.  The  inspection  of  the  map  will  show  numerous  cases 
where  even  in  the  same  lot  one  or  more  trees  were  untouched  while 
the  rest  were  defoliated.  It  does  not  show  many  other  cases  where 
these  favored  trees  were  finally  cut  down,  but  not  till  after  they  fur- 


Fig.  9.     One  of  numerous  undefoliated  trees. 


nished  winged  insects  to  infest  neighboring  trees  just  coming  out  again 
into  foliage. 

In  the  map  and  in  most  of  the  discussion  above,  the  citrus  trees 
alone  have  been  considered.  These  alone  have  been  cut  out  with  any 
attempt  at  thoroughness.  Some  of  the  other  food  plants  have  been 
quite  as  heavily  infested  as  any  of  the  orange  trees. 

The  original  order  of  the  State  Commissioner  did  not  include  all. 
The  newspaper  articles  urging  active  work  have  usually  been  quiet  in 
reference  to  other  food  plants,  and  the  people  generally  seem  to  have 
lost  sight  of  the  fact  that  the  defoliation  of  such  plants  is  quite  as 


11 

important  as  the  orange  trees.  The  fig  is  extremely  abundant  in 
Marysville,  and  is  known  to  furnish  food  for  the  young  insect,  but 
practically  nothing  has  been  done  towards  defoliating  these  trees. 
This  is  a  case  of  an  occasional  food  plant,  for  we  have  not  seen  a  single 
infested  fig-leaf  in  Marysville.  The  insect  evidently  prefers  the 
orange,  but  it  is  certainly  not  wise,  when  complete  eradication  is  at- 
tempted, to  utterly  neglect  a  possible  source  of  reinfestation  of  the 
orange  trees.  Figs  and  oranges  are  in  immediate  contact  all  over  town, 
an  example  of  which  is  shown  in  fig.  10. 


Fig.  10.     Adjacent  Fig  and  Orange  trees,  the  latter  defoliated. 


New  foliage  on  the  trimmed  orange  trees  was  reported  in  the 
Marysville  papers  by  the  10th  of  July,  and  was  to  be  seen  even  earlier 
than  that.  It  is  now  to  be  found  in  all  parts  of  the  town,  as  shown  on 
the  map,  where  only  the  more  conspicuous  examples  were  noted.  In 
many  cases  the  new  shoots  are  over  a  foot  long,  and  some  quite  two 
feet  long.  In  such  cases  the  young  leaves  have  been  subject  to  rein- 
festation for  a  full  two  weeks  at  the  date  of  this  writing.  Those  in 
charge  of  the  work  are  still  trying  to  force  further  defoliation.  Under 
the  circumstances  it  is  hard  to  see  how  any  good  purpose  could  be 


12 

served  by  further  action  at  this  time.  The  opportunity  for  effective 
work  along  these  lines  is  past;  now  we  are  face  to  face  with  new' 
conditions. 

What  to  Do  Next. 

Some  are  ready  to  advocate  that  we  do  nothing.  They  are  ready 
to  trust  to  the  chance  that  it  may  not  spread  from  Marysville  into  the 
orchard  districts,  or  if  it  gets  there,  that  it  may  find  the  conditions 
unfavorable  to  it,  or  that  some  parasitic  insects  may  be  discovered  that 


Pig.  11.     Defoliated  tree  coming  into  foliage. 


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13 

will  render  it  innocuous,  or  some  other  contingency  making  its  de- 
struction unnecessary. 

Granting  that  any  or  all  of  these  contingencies  may  occur,  it  is 
nevertheless  the  part  of  wisdom  to  make  a  determined  fight  as  long  as 
there  is  a  reasonable  chance  that  it  may  be  exterminated. 

The  failure  of  the  past  campaign  need  not  dishearten  us  in  any 
particular,  for,  as  the  account  of  the  work  given  above  clearly  indi- 
cates, the  management  of  the  past  campaign  has  been  fundamentally 
bad,  and  its  history  chiefly  useful  in  pointing  out  how  not  to  do  the 
work. 

There  are  only  two  periods  of  the  year  when  the  eradication  of  the 
white  fly  can  be  undertaken  with  any  reasonable  hope  of  success. 
They  are  the  two  periods  when  all  the  individuals  are  attached  to  the 
leaves  and  possess  neither  wings  nor  legs.  The  longest  and  best  period 
for  the  work  is  during  the  winter.  While  the  insects  may  be  able  to 
feed  and  grow  during  this  period,  coming  gradually  to  full  size,  they 
are  finally  brought  to  a  standstill,  being  unable  to  transform  into  the 
winged  condition  until  the  weather  is  warmer.  Thus  it  comes  about 
that  the  insects  that  were  of  all  sizes  in  the  fall,  reach  the  winged  con- 
dition in  the  spring  at  the  same  time.  Both  preceding  and  following 
this  great  spring  brood  of  flies  there  is  a  period  when  all  are  wing- 
less. All  through  the  month  of  May  and  well  into  June  the  insects 
of  this  spring  brood  were  on  the  wing,  and  laying  eggs.  Some  of  the 
young  hatching  from  these  eggs  were  fully  a  month  older  than  the 
youngest  members  of  the  family.  Thus  there  is  only  a  brief  period 
during  which  successful  work  could  be  done.  The  quiescent  period  of 
winter  is  much  longer. 

From  early  in  July,  through  the  remainder  of  the  summer  and 
probably  until  killing  frosts  come,  the  insect  is  continually  on  the  wing, 
owing  to  the  overlapping  of  broods,  rendering  eradication  at  this  time 
hopeless. 

Summer  Work. 

While  the  insect  cannot  be  eradicated  at  this  time  of  the  year,  there 
is  much  important  work  to  do,  upon  the  doing  of  which  the  success  of 
next  winter's  campaign  will  depend. 

The  man  put  in  charge  of  the  work  should  begin  at  once,  and  have 
a  sufficient  number  of  assistants  to  do  it  thoroughly.  These  assistants 
should  be  selected  for  three  different  classes  of  work,  and  each  group 
put  in  immediate  charge  of  an  expert  in  that  particular  line.  These 
three  lines  of  work  should  be  as  follows : 


14 

First — A  horticultural  staff  should  be  selected,  whose  first  work 
should  be  to  assist  the  people  of  Marysville  in  making  trees  again  out 
of  the  stumps  now  standing.  They  are  in  need  of  expert  assistance. 
This  staff  must  prove  to  the  citizens  of  that  town  that  they  are  endeav- 
oring to  be  genuinely  helpful,  that  this  campaign  will  be  managed 
with  their  interests  uppermost.  They  will  also  make  themselves  fa- 
miliar with  every  detail  of  the  situation  and  be  ready  to  take  immediate 
charge  of  the  defoliation  of  next  winter. 

Second — There  should  be  a  staff  of  inspectors,  working  both  in 
Marysville  and  the  surrounding  country,  continually  on  the  search  for 
infested  trees.  The  work  of  this  staff  will  have  to  be  continued  for  at 
least  a  year  after  the  last  white  fly  is  seen. 

Third — A  staff  of  investigators  should  make  an  exhaustive  study 
of  the  habits  of  the  fly,  particularly  testing  out  experimentally  the 
possible  range  of  the  food  habits  of  the  insect.  We  ought  to  be  in  a 
position  to  say,  with  full  confidence,  just  what  plants  to  take  into  con- 
sideration in  the  winter  work;  furthermore,  we  must  know,  beyond 
question,  whether  the  insect  can  live  on  fallen  leaves,  as  so  many  species 
of  white  flies  do,  so  that  we  shall  know  what  to  do  with  deciduous  trees. 
Finally,  this  staff  shall  be  the  place  of  appeal  for  the  other  depart- 
ments of  the  work. 

The  summer  work,  as  outlined,  is  necessary  to  make  a  sound  foun- 
dation for  the  winter's  campaign. 

Winter  Work. 

The  character  of  the  winter  work  has  been  foreshadowed  in  de- 
scribing that  of  the  summer.  The  exact  course  to  follow  will  depend, 
in  a  large  measure,  on  the  results  of  the  summer's  investigation.  Cer- 
tain general  plans  can,  however,  be  now  given. 

The  horticultural  staff  would  have  to  be  greatly  enlarged  and  sepa- 
rated into  two  divisions.  To  one  would  be  given  the  defoliation  work ; 
to  the  other,  the  cleaning  up  and  disposal  of  infested  material.  The 
latter  division  would  act  as  a  check  upon  the  former  division,  and  the 
staff  of  inspectors  following  them  would  insure  that  all  is  thoroughly 
done. 

This  plan  of  campaign  involves  that  the  actual  work  of  defoliation 
be  done  by  those  in  charge  of  the  work,  and  is  the  only  practical 
method  of  securing  uniformity  and  thoroughness.  The  cost  of  the 
work  should  not  be  assessed  against  the  owners  of  the  properties  in- 
volved.    The  work  of  defoliation  should  be  completed  as  soon  as  pos- 


15 

sible  after  all  eggs  are  laid  in  the  fall  and  the  winged  forms  have 
disappeared. 

A  programme  of  work,  like  that  outlined  above,  does  offer  some 
hope  of  the  eradication  of  the  pest ;  but  unless  ample  provision  is  made 
for  it  and  scientific  accuracy  and  thoroughness  insured  by  the  appoint- 
ment of  the  right  kind  of  men  to  organize  and  direct  the  same,  satis- 
factory results  will  not  be  secured. 


